I think the real answer is that the Schwartzian Transform is only applicable when you truly have an expensive key extraction that swamps the overhead of making copies, creating references and dereferencing them, etc. Your non-copying approach would only be valid when the expense of copying is significant. It doesn't change the fundamental purpose of the transform, which is is save on the O(n lg n) portion at the expense of the O(n) portion.

If you do have expensive copying, or just a not-very-expensive key extraction, then a better approach would be to eliminate both the copying and all of the reference stuff in one shot, by using indexes instead. Try adding this code into the benchmark: